It has been conventional to form a cut called notch on an outer circumference of a wafer such as a single crystal silicon wafer having a diameter of 300 mm or more in order to align the wafer in a manufacturing process. The wafer is sliced along a certain crystal orientation so as to make the crystal structure most appropriate for the operation of a semiconductor device to be manufactured. The notch position is determined, depending on a conductivity type and a crystal orientation, in a direction of the crystal orientation such as <110> and <100>.
Recently, along with a high integration of a semiconductor device such as DRAM, NAND flash memory, and MPU and a diameter enlargement of a wafer, there is increased a stress applied to the wafer during heat treatment in the process for manufacturing a semiconductor device, and there arises a problem of slipping, which causes a junction leak. In particular, the stress concentration is easily generated at a portion having a local shape such as a notch, easily causing slipping. Therefore, device makers have demanded a wafer having no cut such as notch.
In the method for manufacturing a silicon wafer used as a semiconductor memory device material, first, a silicon crystal ingot having a specific crystal orientation is produced by the Czochralski (CZ) method or other method (a crystal growing process). Then, the produced single crystal ingot is ground to adjust the outer diameter, and a notch for indicating the crystal orientation is formed on an outer circumference of the single crystal ingot (a cylindrical grinding process). Then, the single crystal ingot is sliced into a thin disk-shaped wafer along the specific crystal orientation (slicing step), and an outer circumference of the sliced wafer is chamfered to prevent the wafer from cracking and chipping (a chamfering process).
Thereafter, both surfaces of the chamfered wafer are flattened by grinding (a double-disc grinding process), and mechanical damage remaining in the wafer chamfered and double-side polished is removed (an etching process). Further, the front surface and/or the back surface of the wafer are mirror-polished (a polishing process), and the polished wafer is cleaned to remove a polishing agent and foreign substances attached thereto (a cleaning process).
The method for manufacturing a wafer having no notch (notchless wafer) by the above manufacturing process includes, as shown in FIG. 5, stamping a crystal orientation mark on the back surface of the double-disk ground wafer by laser marking with reference to the notch (a laser marking process) and removing the notch by grinding the outer circumference of the laser-marked wafer (a notch removing process) (see Patent Document 1). A crystal orientation mark M shown in FIG. 6 formed by laser on the back surface of the wafer W instead of the notch is under development by Semiconductor Equipment and Materials Institute (SEMI).